The present disclosure relates to uranium contamination treatment, and specifically it is a comprehensive joint technology-based device and method for the treatment of uranium-contaminated soil.
With China's increasingly rapid exploration and mining of uranium, there emerge numerable uranium tailings and waste ores. Currently, the dedicated storage facility of uranium tailings is the uranium tailings impoundment. According to incomplete statistics, the total amount of uranium tailings worldwide has reached 20 billion tons. Since 1940s, uranium and other radionuclides from a large quantity of in-service or retired uranium tailings have went into the ground water, and flowed and spread with the groundwater, causing serious harm to the ground water and the ecological environment. Uranium is primarily a a-ray source (uranium-235 is 4.679 MeV, uranium-238 is 4.270 MeV), and its half-life period is up to a million years (the half-life of uranium-235 is 704 million years, and the half-life of uranium-238 is 4.46 billion years), with an extremely slow convection velocity. Uranium in the soil will be accumulated in the human body due to the bioaccumulation action, while its chemical behavior and physiological toxicity are similar with lead, which means it will cause chemical toxicity to human and animal kidney. When the volume of uranium in human body is over 3 mg/kg, it will do harm to human body or even cause cancer.
The soil contamination caused by uranium is mainly of three kinds. The first kind of contamination is caused by the test and use of depleted uranium bombs. For example, the UK and the US once conducted the depleted uranium bomb tests, respectively leading to 45 t and 70 t depleted uranium substances left in the environment. The second kind of contamination is caused by the production and test of nuclear weapons. The contaminated soil caused by the nuclear weapon production of US Department of Energy is estimated to be 3.0×107-8.0×107 m3, and the contaminated water is of 1.8×109-4.7×109 m3. The third kind of contamination is caused by waste water, waste gas, waste residue, etc. discharged by nuclear power plants. On Mar. 11, 2011, an explosion occurred in Fukushima Daiichi, which used uranium-235 as the fuel for nuclear reactor, and the leaked radioactive material—uranium received much concern all over the world. The fourth kind of contamination is caused by waste residue of uranium tailings. The volume of uranium tailings waste is estimated to reach 9.38×108 m3 due to the uranium mining. China's uranium mines are located in more than 30 counties of 15 provinces and cities nationwide, ⅔ or more of uranium mines are located in mountainous, humid and rainy regions, while nearly ⅓ are located in hills and arid regions. Over the years, the total amount of waste ores mined from uranium mines are about 28 million tons, covering an area of 250 hm3. And uranium tailings charged by waste water treatment plants are about 30 million tons, which is covering an area of 375 hm3 if calculated as its average stacking height of 4 m.
Uranium exists in the soil in an adsorbed state (in soil particles and pore water), the compound state, the sediment state and the exchangeable state, while these sates will greatly affect the uranium migration. Due to the huge nuclear pollution hazards, the depollution of nuclear contamination in a large scale is a worldwide problem. All walks of life are looking for ways to clear nuclear contamination, and they have achieved some results. The depollution methods adopted by most countries include: physical methods, chemical methods, electrochemical methods, physical-chemical methods, microbial clearance and soil nuclear contamination removal method, but these methods are usually of a high cost and easy to cause a secondary pollution to the environment, failing to solve the problem of radionuclides removal fundamentally. Although the forest restoration method can remedy the contaminated soil in a large scale, and can be used for the development of industrial raw material forest and firewood forest, but its required radionuclide concentration can only be at a not high level, greatly restricting its application. Foreign scholars mainly adopt chemical method for the treatment of uranium-contaminated soil, for example, Caroline et. al (1998) uses sodium bicarbonate for the extraction of uranium in soil solution, and then adopts the ion exchange technology to remove the uranium in the soil solution. Kantar et al. (2006) points out that the citric acid elution technique can be used to improve the clearance efficiency of uranium in soil under the weak acid condition. And Crean et. al (2013) uses multi-level chemical extraction techniques for the remediation of depleted uranium particles in contaminated soil. Currently, in China, researches on the uranium-contaminated soil are mainly focused on bioremediation, for example, the patent CN200810030860.4 discloses a method of using American phyotalacca acinosa seedling for the treatment of the soil contaminated by uranium tailings; patent CN201210056468.3 discloses a method of using water spinach for the treatment of soil contaminated by high-concentration uranium, and the patent CN201210155561.X discloses a method of using fertilizer to promote the treatment of soil contaminated by uranium or cadmium with broad beans.